1. Field of the Invention
The invention relates to the manufacture of camshafts for internal combustion engines.
A camshaft for an internal combustion engine has a shaft carrying a number of cams which have a required angular and axial inter-relationship. The cams have surfaces with a predetermined profile and have to be particularly wear-resistant, since they are repeatedly striking associated tappets. The traditional way of manufacturing camshafts is by casting or forging, but this can be timeconsuming and expensive.
2. Review of the Prior Art
A recent proposal has been to form the cams separately from the shafts and then connect them together. This allows the cams to be made from a first material and by a first technique and the shafts to be made from a different material and/or by a different technique. One example of this is where the cams are made of a sintered metal powder with a highly wear-resistant surface and where the shaft (which may be solid or may be a tube) is made from a less expensive material, such as a mild steel, machined or forged or extruded to shape.
Such camshafts have the problem, however, that the cams must be very accurately positioned on the shaft before they are connected to them and that their shaft-engaging holes must be truly concentric--because any out of concentricity will be reflected in an inaccurate positioning of the associated cam. Hitherto, it has been proposed to connect individually finished cams to a shaft by welding or by the use of pins passing through the cams into the shaft. These manufacturing methods can, however, be time-consuming or expensive and do not deal with the problem of concentricity.